package main

import (
	"fmt"
)

func main() {

	//1, 1, 2, 3, 5, 8, 13, 21
	n := 5

	first := 1

	second := 1

	ret := 0

	for i := 3; i <= n; i++ {

		ret = first + second

		first = second

		second = ret

	}

	fmt.Println(ret)
}
